Viha is a current graduate student at Carnegie Mellon, studying information security. She lives with 2 roommates in a Squirrel Hill apartment. One of the benefits of having roommates is that even if she forgets to buy milk, her roommates would help replenish. However, she doesn't want to always rely on her roommates.
Unfortunately, even when Viha does go grocery shopping, she often realizes that she forgot to buy milk only after coming back from the grocery store.
When visiting her home, we discovered that one of her favorite objects is her collection of fridge magnets. Her fridge magnets hold up important information and papers with sentimental value for her. We thought communicating how much milk is left could be a useful capability for a fridge magnet, as it lives in a very visible place at home. We also chose to create a fridge magnet because we want to add to her collection, instead of introducing an item that may feel unfamiliar to her.
Our goal: Functionally, we want to create a device that can proactively remind Viha when her milk is running low, so she will remember to buy milk. Visually, the device should look like it is part of her home environment, and not like a foreign object.
Design approach
Magnet size: We decided that the device needed to be big enough for Viha to see the neopixel color feedback clearly, but small enough to still feel like a magnet.
Size of neopixel: It should be big enough so that Viha can see the colors clearly close up as well as when she is 80'' away (glancing at the fridge on her way out the door).
Visual design of the milk carton: From observing the items Viha has in her room, she likes objects that are cute and animated-looking. This inspired us to take on a cartoon-y aesthetic for the visual design of the milk carton.
Engineering approach
To enable the fridge magnet to detect the milk, we used a bar type load sensor. The load sensor with a maximum rated capacity of 5 kgs was chosen as a typical one gallon milk carton weighs at around 4.3 kgs. To detect the level of milk in the fridge, the sensor reads the instantaneous value every second and publishes that to the cloud. The fridge magnet subscribes to the event and sends signal to the neopixel to display different colors as mentioned in the schematic diagram as shown above. A 1200 mAh LiPo battery is connected to the neopixel circuit.
We learned that Viha frequently buys 1 gallon of milk, but sometimes there are times when she has to settle for smaller volumes if the gallon milk runs out at the grocery store. This made us realize that we need to calibrate the scale to address low, medium, and high volume for each of the carton size she could buy. The 2nd feedback was she always places her milk on the bottom shelf. The wiring between the fridge magnet and load sensor stretched across the fridge shelves, making it inconvenient for her to reach items. In our next iteration, we will try to make the load sensor wireless. Lastly, Viha doubted whether the load sensor is sturdy enough to sustain the weight of a gallon’s milk. From a function perspective, the load sensor works well with a gallon, but we might make it look wider visually to help Viha feel at ease.
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